Friction contrafibulator
The friction contrafibulator was a button on the console of the Doctor's TARDIS. When Vincent van Gogh attempted to touch it, the Eleventh Doctor leapt across the TARDIS to stop him. (TV: Vincent and the Doctor)
Later, he used the button to stabilise the TARDIS interior when confused by the presence of the Eleventh, Tenth, and War Doctors. (TV: The Day of the Doctor)
Behind the scenes
Though the word is superficially technobabble, it's also a subtle connection to another Richard Curtis script: Blackadder the Third's Ink and Incapability. In that story Blackadder frustrates lexicographer Samuel Johnson by throwing out a few nonsense words — including contrafibularity — after Johnson has claimed that his dictionary contains "every single word" in the English language.
Breaking down this non-word to its real components, we find that it means contra (against) + fibula (the smaller of the two major bones of the leg) : "pulling one's leg".
